La barre



June 12, 1956 F. LA BARRE, JR.. ET AL 2,7

PROPELLER PROTRACTOR Filed NOV. 5, 1953 3 Sheets-Sheet 1 INVENTORS FLOYD[/4 BAPAf/E, FRANK J (HU/P/VELL,

W/LJONO/VAGLE, ANT/IONVPPfA/NOUC TTO NEYS.

June 12, 1956 Filed Nov. 3, 1953 F. LA BARRE, JR., ET AL PROPELLER PROTRACTOR- 3 Sheets-Sheet 2 IN VENTORS. FL 0V0 M EABPEJB, FRANKJ C/fU/PVFZL,

W/LJO/VDA/A 61E, ANTI/MVP PtW/VOOK BY 0 I ATT RNEYS,

United States Patent PROPELLER PROTRACTOR Floyd La Barre, Jr., Denville,Frank J. Churnell, Bloomfield, Wilson D. Nagle, Fair Lawn, and AnthonyP. Pennock, Flor-ham Park, N. J., assignors to Curtiss- WrightCorporation, a corporation of Delaware Application November 3, 1953,Serial No. 390,042

8 Claims. (Cl. 33-180) This invention relates to aircraft propellers andin particular, to measuring equipment by which the pitch setting ofaircraft propeller blades may be readily measured while the propellerisinstalled on an aircraft.

The invention provides a propeller blade protractor assembly which maybe used for any or all of the blades of single or dual rotationpropellers, enabling accurate determination and corelation of propellerblade pitch angles. On dual rotation propellers, the blades of theoutboard propeller may have a slightly different pitch angle settingthan the blades of the inboard propeller, and the pitch angle of theblades of an inboard propeller may vary at a different rate than thepitch angle of the blades of the outboard propeller. A proper protractorserves to confirm that the blades, after propeller installation, areproperly coordinated for the design pitch settings. Frequently, afterinstallation of a dual rotation propeller, it is desirable to check thepropeller pitch angles with respect to a fixed reference.

In the past, some rather complex optical procedures have been utilizedto determine blade pitch angles while the propeller was installed on anaircraft. The present invention enables precise determination of bladepitch angles by the use of a protractor assembly which is designed sothat a plane perpendicular to the propeller axis is used as a referenceplane from which the pitch angle of any propeller blade can bedetermined with great precision. This obviates the need for using levelbubbles, plumb lines, or other references which are not directlyassociated with the propeller installation.

Objects of the invention are to provide a readily portable. propellerblade protractor assembly which may be installed on, and utilized forthe determination of the pitch angle of, any propeller blade when itspropeller is in operating position in an aircraft. A further object ofthe invention is to provide a protractor assembly of more or lessuniversal utility, so that, using appropriate adapters, the basicprotractor assembly can be used for propeller blades of a wide varietyof sizes and designs.

The specific nature and details of theinvention can better beappreciated by reading the following detailed description in connectionwith the attached drawings, in which similar reference charactersindicate similar parts, and in which:

Fig. 1 is an elevation of the invention in use on the outboard propellerof a dual rotation propeller system,

Fig. 2 is an elevation similar to Fig. 1 wherein the pitch angle of aninboard propeller blade is being determined,

Fig. 3 shows the invention applied for pitch angle determination on asingle rotation propeller,

Fig. 4 is an enlarged plan of the invention adjuste as in Fig. 1 andshowing additional details,

Fig. 5 is a section on the line 55 of Fig. 4, and

Fig. 6 is a plan of a part of the invention as adjusted for use with aninboardpropeller of a dual rotation system.

In Figs. 1 and 2, in dotted lines, we show a power plant nose 10 uponthe propeller shafts of which are mounted an inboard propeller 12 and anoutboard propeller 14. The inboard propeller has blades 16 extendingtherefrom, and the outboard propeller has blades 18 extending therefrom,the blades as shown having airfoil profile in section.

Referring to Fig. 1, measurement of the pitch angle of the blade 18involves the measurement of the angle between the chord of the blade anda reference line or plane. An appropriate plane is one which isperpendicular to the axis of rotation of the propellers and which thuslies parallel to the plane of rotation of the propellers, such planebeing indicated at 20. Some particular station along the propeller bladeis normally specified as one at which pitch angle readings are to betaken. Since any conventional propeller blade twists slightly from itsroot toward its tip, it is necessary for com parison and standardizationto measure the pitch angle of all blades at a standard station, ordistance of the blade section from the center of rotation. Before makingthe pitch angle determination, each blade is appropriately marked toidentify the standard station. Thereupon, a protractor assembly 22 isslipped over the end of the propeller blade, the protractor assemblyincluding a member 24 having an aperture 25 to receive the blade. Themember 24 includes anvils 26 and 28 which rest on the thrust face of thepropeller blade, there also being a stop 30 which is engaged with theleading edge of the propeller blade. A clamp 32 on the member 24 is thenscrewed down upon the camber surface of the propeller blade so that themember 24 is held firmly, in fixed attitude, relative to the blade.

A member 34 is pivoted to the member 24 at 36, a portion of the memberhaving a Vernier scale 38 which registers with angle graduations 40inscribed on the member 24. The member 34 may be swung on its pivot andmay be clamped in any position by a screw clamp 42 operating inconjunction with a slot 44 on the member 24. The member 34 is furtherprovided with a plane plate 46. To determine the pitch angle of theblade 18, the member 34 is moved about its pivot until the plane of theplate 46 is coincident with the plane 20 which is perpendicular to thepropeller axis of rotation.

To establish this parallelism relationship between the planes 20 and 46,a member 48 is slipped over the inboard propeller blade 16,' the member48 having an aperture 50 within which the blade is received, and havinganvils 52 and a clamp 54 by which the member 48 is firmly secured to theblade 16. To the member 48 is secured a dial indicator 56 whose movablestem 58 is alined so that it can engage the plate 46 of the assembly 22.i

With the protractor 22 installed on the blade 18 and the member 48installed on the blade 16, the propellers 12 and 14 may be oscillatedrelative to one another about their axes so that the dial indicator stem58 moves back and forth along the plate 46. If the dial indicatorreading varies during this oscillation, it shows that the plate 46 isnot coincident with the plane 20. Thereupon, the member 34 may be movedabout the pivot 36 to a position of adjustment where the dial indicatorwill indicate zero change as it sweeps along the plate 46 duringrelative oscillation of the two propellers. When this adjustment isreached, the plate 46 lies in a plane perpendicular to the propelleraxis and establishes the member 34 as a reference member from whichblade pitch readings may be taken. The blade pitch reading is thenobserved on the. angle marks 40 and precise pitch angle is establishedby using the Vernier scale 38. Normally the scales 38 and 40 would be socalibrated that pitch angles of .01" may be ascertained.

The foregoing description relates to the measurement of pitch angles onthe outboard propeller of a dual rotation system. To measure the pitchangles on the inboard propeller, as shown in Fig. 2, the member 22 isinstalled on the inboard blade 16 and the member 48 is installed on theoutboard blade 18. The same adjustment procedure in undertaken and whenthe plate 46 is perpendicular to the propeller axis, the blade pitchangle of the inboard blade 16 may be read on the scales 38, 40.

By installation of the equipment consecutively on the several blades ofthe propeller, the pitch angle settings of all blades may beascertained.

For a single rotation propeller, the protractor assembly 22 may beinstalled as previously described, and the dial indicator 56 may besecured to a bracket 60 secured in any appropriate manner as by a bolt62 to the engine structure, providing a fixed mounting for theindicator. By oscillating the propeller and adjusting the plate 34 inthe manner previously described, an accurate reading of pitch angle forthe propeller blade may be had. In this case, the single rotationpropeller is numbered 64 and its blades are noted as 66. Otherwise, thecomponents of the assembly 22 may be identical with those previouslydescribed.

Referring to Figs. 4-6, details of the protractor assembly are shown. InFigs. 4 and 5, the reference member 48 includes two posts 70 and 72 onopposite sides of the member, the latter being formed from a fiatmetallic plate. The post 70 carries the clamp 54, and the post 72carries a. clamp 54', each having a pad 74 for engagement with onesurface of a propeller blade such as 16. The two clamps enableattachment of the member 48 to the propeller blade without rocking,there being four points of contact of the member 48 with the blade.These points comprise the two anvils 52 and the two pads 74.

The assembly 22, constituted by the members 24 and 34, includes twoblocks 78 and 80 secured on opposite sides of the plate member 24, theseblocks holding the screw clamps 32 and 32. The screw clamps carry pads82 which are engaged with the camber surface of the blade 18, and areopposed by the two anvils 26 and 28 which engage the thrust face of thepropeller blade. Thereby, the assembly 24 is securely held on the bladeat four points of contact, so that the reference plate 46 may beadjusted so that it lies in parallelism with a plane normal to thepropeller axis.

Preferably, the anvils 26 and 28 and the stop 30 are all set up on atemplate 84 which is clamped to the member 24 by clamps 86. A template84 is prepared for each type of propeller blade and the appropriatetemplate for the type of blade to be calibrated is installed on themember 24 when a pitch angle measurement is to be made. Individualcharacteristics of the airfoil section of the propeller blade make itmost convenient to use a template such as 84 since the template includescompensations for any angular difference between the chord line of theblade section and the form of the thrust face of the propeller blade,the latter not necessarily being flat.

Fig. 4 shows the template 34 and the clamps 32 and 32 installed on theassembly 22 for use with a propeller rotating in a counterclockwisedirection. The template is located by pads 85 permanently fixed on themember 24, and the clamp blocks for clamps 32 and 32 are secured tomember 24 at location 87.

When the protractor assembly is to be used for a clockwise rotatingpropeller assembly, the member 22 must be turned over as shown in Fig.6. Herein, the template 84 is transferred from its previously describedattachment points at locations 85 on the member 24 to another set ofattachment points 90 on the opposite side of the aperture 50 in themember. Also, the clamp blocks 78 and 80 are transferred from theoriginal location 87 to a location 92. This enables the anvils 26 and 28and the leading edge stop 30 of the template 84 to engage the bladesection at proper points on and adjacent the thrust face of thepropeller blade 16 so that the relationship of the anvils 26 and 28 iscorrect, with respect to the chord line of the propeller blade section.

When the assembly 22 is used on an inboard propeller, as shown in Fig.6, the member 34 is adjusted to bring the plate 46 into a plane normalto the propeller axis. The scales 38 and 40 face toward the propellerhub rather than toward the propeller tip as in Figs. 1, 3 and 4.However, this mode of reading the scales, from the hub side rather thanfrom the blade tip side, injects no dificulty in using the protractorapparatus effectively.

So far as the reference member 48 is concerned, the anvils 52 and theclamp 70 need not be interchanged when such member is shifted from aninboard propeller blade to an outboard propeller blade, since the member48 is used simply as a stable mounting for the dial indicator 56. Itmatters little whether the anvils 52 engage the thrust face or thecamber face of the blade, so long as the member 48 is held securely onthe blade.

The invention has been shown and described as for use when a propelleris fully assembled and mounted, as on a power plant. However, theinventive scope is deemed to include the claimed protractor when used onan uninstalled propeller. For instance, the dial indicator 56 may becarried by a blade of a dual rotation propeller when the latterconstitutes an integral assembly, or when its components are mounted ona test spindle whose axis is coincident with the propeller axis. Or, thedial indicator could be mounted on the power unit of the propeller whichordinarily is coaxial therewith and rotatable relative thereto. In anyutilization, it is feasible to secure the dial indicator on the member34, and to dispose the plate 46 on the reference structure so that itprovides a reference plane normal to the propeller axis of rotation.

The invention herein described may be modified in specific form withoutdeparting from the spirit or scope of the invention but it will be clearfrom the foregoing that the pitch angles of propeller blades for eithersingle or dual rotation propellers may be accurately determined byproper use of the several items of equipment which constitute theprotractor assembly.

Though a single embodiment of the invention is shown, it is to beunderstood that the invention may be applied in various form and invarious environments. Changes may be made in the arrangement shownwithout departing from the spirit of the invention. Reference should behad to the appended claims for definition of the limits of theinvention.

What is claimed is:

1. A protractor for determining the pitch angle of a propeller bladewhen rotatably installed on an aircraft, comprising a member clamped tothe propeller blade, a second member pivoted to the first member, saidtwo members having interrelated indicia thereon to indicate the relativeangular relation therebetween, said second member having a planarreference portion, the second member being adjustable relative to thefirst member finally to disposed said planar reference portion in areference plane parallel to the propeller plane of rotation, and anindicator device secured to the aircraft and having a point contactorpart in said reference plane and engageable with consecutively withseveral points on said reference portion as said blade is rotatedrelative to said aircraft to gauge the alinement of said portion in saidreference plane.

2. A protractor for determining the setting angle of a blade assembledin a hub journalled for rotation on a structure, comprising a memberincluding clamps for attaching the member to the blade, a second memberpivotally mounted on said first member and including at least two basereference points, reference means adapted to be secured to saidstructure and comprising a point contactor, said second member beingadjustable on its pivot to aline said base reference points in the sameplane as the contactor of said reference means as said blade and hub arerotated about the hub axis relative to said structure, said planedefined by said alignment of said base points lying normal to the hubrotational axis, and scale indicia on said members calibrated to enablereading of the relative angularity of said members.

3. A protractor for determining the setting angle of a blade assembledin a hub journalled for rotation on a structure, comprising a memberincluding clamps for attaching the member to the blade, a second memberpivotally mounted on said first member and including at least two basereference points, reference means adapted to be secured to saidstructure and comprising a point contactor, said second member beingadjustable on its pivot to aline said base reference points in the sameplane as the contactor of said reference means as said blade and hub arerotated about the hub axis relative to said structure, said planedefined by said alignment of said base points lying normal to the hubrotational axis, and scale indicia on said members calibrated to enablereading of the relative angularity of said members, said first memberincluding detachable locating elements to adapt the protractor to aparticular form of blade.

4. A protractor for determining the setting angle of a blade assembledin a hub journalled for rotation on a structure, comprising a memberincluding clamps for attaching the member to the blade, a second memberpivotally mounted on said first member and including at least two basereference points, reference means adapted to be secured to saidstructure and comprising a point contactor, said second member beingadjustable on its pivot to aline said base reference points in the sameplane as the contactor of said reference means as said blade and hub arerotated about the hub axis relative to said structure, said planedefined by said alignment of said base points lying normal to the hubrotational axis, and scale indicia on said members calibrated to enablereading of the relative angularity of said members, said structurecomprising in part, another blade axially spaced from the first bladeand rotatable in a plane parallel thereto, and said reference meanscomprising a dial indicator adapted to be secured to said another blade.

5. For use with a dual rotation aircraft propeller comprising coaxialinboard and outboard oppositely rotatable hubs each having pitchedblades extending therefrom, a protractor assembly comprising meanssecured to a blade of one hub carrying a dial indicator whose movablestem is directed toward the plane of rotation of blades of the otherhub, a member secured to a blade of the other hub, a second memberpivoted to said first member having a surface engageable by the stem ofsaid dial indicator, said second member being adjustable to bring saidsurface into a plane parallel to the planes of rotation of said blades,and means to indicate the angular relation of said two members.

6. For use with a dual rotation aircraft propeller comprising coaxialinboard and outboard oppositely rotatable hubs each having pitchedblades extending therefrom, a protractor assembly comprising meanssecured to a blade of one hub carrying a dial indicator whose movablestem is directed toward the plane of rotation of blades of the otherhub, a member secured to a blade of the other hub, a second memberpivoted to said first member having a surface engageable by the stem ofsaid dial indicator, said second member being adjustable to bring saidsurface into a plane parallel to the planes of rotation of said blades,and means to indicate the angular relation of said two members, saidfirst member including a template removably secured thereto whichengages the blade at two points along the chord surface and at theleading edge, and clamps on said member engageable with the cambersurface of the blade by which the member is secured to the blade.

7. For use with a dual rotation aircraft propeller comprising coaxialinboard and outboard oppositely rotatable hubs each having pitchedblades extending therefrom, a protractor assembly comprising meanssecured to a blade of one hub carrying a dial indicator whose movablestem is directed toward the plane of rotation of baldes of the otherhub, a member secured to a blade of the other hub, a second memberpivoted to said first member having a surface engageable by the stem ofsaid dial indicator, said second member being adjustable to bring saidsurface into a plane parallel to the planes of rotation of said blades,and means to indicate the angular relation of said two members, saidfirst member including a template removably secured thereto whichengages the blade at two points along the chord surface and at theleading edge, and clamps on said member engageable with the cambersurface of the blade by which the member is secured to the blade, saidtemplate and clamps being movable to alternate mounting positions onsaid member to hold the member in correct relationship on a propellerblade adapted for opposite rotation.

8. For use with an aircraft propeller comprising a hub having pitchedblades extending therefrom and rotatably mounted relative to astructure, a protractor assembly comprising means secured to saidstructure carrying a dial indicator whose movable stem is directedtoward the plane of rotation of blades of the propeller, a membersecured to a blade of the propeller, a second member pivoted to saidfirst member having a surface engageable by the stem of said dialindicator, said second member being adjustable to bring said surfaceinto a plane parallel to the plane of rotation of said blades, and meansto indicate the angular relation of said two members.

References Cited in the file of this patent UNITED STATES PATENTS2,059,407 Spase Nov. 3, 1936 2,170,493 Clapper Aug. 22, 1939 2,170,824Lichtenwalner Aug. 29, 1939 2,402,567 Milner June 25, 1946 2,481,062Anderson Sept. 6, 1949

